In an imaging apparatus using an image sensor, vertical line-shaped fixed pattern noise appears in a specific portion of an image outputted from the imaging apparatus in some cases. For example, in an imaging apparatus using a CMOS image sensor, vertical line-shaped noise appears due, for example, to an offset error in an A/D converter that performs parallel processing on a column basis. In an imaging apparatus using a CCD image sensor, on the other hand, vertical line-shaped noise sometimes appears, for example, when high-frequency horizontal transfer pulses are used and the horizontal transfer pulses meet a specific phase condition.
The thus produced vertical line-shaped noise can be removed by detecting an offset component that is the source of the noise and subtracting the offset component from pixel signals. The offset component is present not only in outputs from pixels in an effective pixel area but also in outputs from pixels in an optically black area (hereinafter also referred to as OPB area). In view of the fact, optically black signals (hereinafter also referred to as OPB signals) outputted from pixels in the OPB area are used in related art to detect the amount of the offset component, that is, a vertical line level and produce a correction value used to remove the vertical line-shaped noise. The vertical line-shaped noise can be removed by multiplying effective pixel signals outputted from pixels in the effective pixel area by the thus produced correction value.
Part of the OPB area, which has a vertical shape and is so blocked that light is not incident thereon, is in many cases used as an area from which vertical line levels are detected, specifically, an area having a width corresponding to the number of lines in the effective pixel area. In the period during which the area is scanned, OPB signals read from the pixels in the area are used to detect a vertical line level and produce a correction value, which is used to process effective pixel signals from the lines in the effective pixel area. The vertical line-shaped noise can thus be removed in real time while images are captured at the same time. In the method described above, however, the absolute number of locations where a vertical line level is sampled is small, resulting in decrease in precision in detection of the vertical line level. That is, vertical line-shaped noise will not be corrected in a satisfactory manner.
As a method for improving the precision in detection of a vertical line level, for example, JP-A-10-313428 describes a method for selecting pixels corresponding to a plurality of horizontal lines in an image sensor, summing outputs from the pixels in the vertical direction, dividing the sums by the number of summed lines to produce averages, and producing correction data by using the averages.